Fallopian tube traveler (4)
'fallopian tube traveler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ovum that I've seen before include "Female gamete" , "Reproductive cell, 'egg' in Latin" , "Female reproductive cell" , "bit of life potentially" , "A female egg-cell" .)
(Other definitions for egg that I've seen before include "Laid item" , "Spur" , "Food from a hen" , "Poacher's requisite" , "Oval item" .)